In all honesty, I think Irene is the only woman who could actually handle Sherlock. Mycroft can barely deal with him and he's Sherlock's brother, Molly doesn't stand a chance, Jim was way too unstable, and John... Well John is special because he's John Watson. Every Sherlock in every incarnation needs his Watson. But Irene really got to him. She took everything he threw at her in stride right up until the very end. That's what makes her character stand out in my opinion.